EP2626598A2

EP2626598A2 - Engines and pistons for them

Info

Publication number: EP2626598A2
Application number: EP13000440.1A
Authority: EP
Inventors: Hiroki Kuwayama; Takahiro Yamazaki; Yutaka Ishigaki; Hideyuki Koyama; Manabu Miyazaki; Yoshinori Tanaka; Keita Naito; Hidetaka Morinaga
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 2012-02-10
Filing date: 2013-01-30
Publication date: 2013-08-14
Anticipated expiration: 2033-01-30
Also published as: EP2626598B1; US9027933B2; JP5893946B2; US20130207350A1; CN103244305B; JP2013164022A; CN103244305A; EP2626598A3

Abstract

An engine in which an oil consumption and a leakage of blow-by gas can be stably reduced for a long period of time has a piston including a first land 3, a first ring groove 4, a second land 5, a second ring groove 6, a third land 7, a third ring groove 8, and a piston skirt 9 formed on a piston peripheral wall 1 in this order from the head of the piston. A first pressure ring 10 is fitted in the first ring groove 4; a second pressure ring 11 is fitted in the second ring groove 6; an oil ring 12 is fitted in the third ring groove 8. A corner at a boundary between an outer peripheral face 5a of the second land 5 and a second-land-side end face 6a of the second ring groove 6 is bevelled, with a tapered face 14 having a diameter reducing toward the second ring groove 6 to form an indentation for the suppression of variation in gas pressure in the space 17 facing the second land during upward and downward movements of the piston.

Description

The present invention relates to an engine and particularly to an engine in which oil consumption and a leakage of blow-by gas can be stably reduced even after operation for a long period of time.
In JP-A-10 (1998)-54297 there is proposed an engine including: a first land, a first ring groove, a second land, a second ring groove, a third land, a third ring groove, and a piston skirt formed on a peripheral wall of a piston in this order from a side of a piston head; a first pressure ring fitted in the first ring groove; a second pressure ring fitted in the second ring groove; an oil ring fitted in the third ring groove; and an indentation formed by a groove in an intermediate portion of an outer peripheral face of the second land.
This type of engine has advantages that a capacity of a space facing the second land increases by a capacity of the indentation of the second land and that variation in gas pressure in the space facing the second land during upward and downward movements of the piston can be suppressed.
However, because the groove in the intermediate portion of the outer peripheral face of the second land forms the indentation of the second land, the rigidity of the second land is significantly reduced, the piston vibrates, and the first ring groove and the second ring groove are liable to be deformed and abnormally worn.
Therefore, though the indentation formed at the second land can suppress the variation in the gas pressure in the space facing the second land during the upward and downward movements of the piston, the vibration of the piston and the deformation and the abnormal wear of the ring grooves make behavior of the first oil ring and the second oil ring unstable and the oil consumption and the leakage of the blow-by gas increase after prolonged operation due to degradation of the sealing performance of the first oil ring and the second oil ring.
An object of the present invention is to provide an improved piston and an engine in which an oil consumption and a leakage of blow-by gas can be stably reduced even after prolonged operation.
The state of the art is as previous indicated. The invention is defined in the independent claims.

Brief description of the drawings

Figs. 1A and 1B are drawings for explaining an engine according to a first embodiment of the present invention, wherein Fig. 1A is a schematic sectional view of a cylinder and a piston and Fig. 1B is an enlarged sectional view of an essential portion; and
Figs. 2A and 2B are drawings for explaining an engine according to a second embodiment of the invention, wherein Fig. 2A is a schematic sectional view of a cylinder and a piston and Fig. 2B is an enlarged sectional view of an essential portion.

General Explanation of the invention

As shown as an example in Fig. 1B, in an engine including: a first land (3), a first ring groove (4), a second land (5), a second ring groove (6), a third land (7), a third ring groove (8), and a piston skirt (9) formed on a piston peripheral wall (1) in this order from a side of a piston head (2); a first pressure ring (10) fitted in the first ring groove (4); a second pressure ring (11) fitted in the second ring groove (6); an oil ring (12) fitted in the third ring groove (8); and an indentation (13) formed at the second land (5),
As shown as an example in Fig. 1B, a corner at a boundary between an outer peripheral face (5a) of the second land (5) and a second-land-side end face (6a) of the second ring groove (6) is planed off with a tapered face (14) having a diameter reducing toward the second ring groove (6) and the tapered face (14) forms the indentation (13) of the second land (5).
As shown as an example in Fig. 1B, because the indentation (13) of the second land (5) is formed by the tapered face (14), the capacity of a space (17) facing the second land increases by the capacity of the indentation (13) formed at the second land (5) and it is possible to suppress variation in gas pressure in the space (17) facing the second land during upward and downward movements of the piston.
Moreover, because the corner at the boundary between the outer peripheral face (5a) of the second land (5) and the second-land-side end face (6a) of the second ring groove (6) is bevelled, i.e. planed off with the tapered face (14) having the diameter reducing toward the second ring groove (6) and the tapered face (14) forms the indentation (13) of the second land (5),the rigidity of the second land (5) is not significantly reduced and it is possible to avoid vibration of the piston (18) and deformation and abnormal wear of the ring groove.
In this way, vibration of the first pressure ring (10) and the second pressure ring (11) can be averted, and high sealing performance of the first pressure ring (10) and the second pressure ring (11) can be maintained. Accordingly it is possible to reduce oil consumption and leakage of the blow-by gas even after prolonged operation.
As shown as an example in Fig. 1B, because an angle (Θ) of the tapered face (14) to a cylinder-side imaginary extension line (6b) of the second-land-side end face (6a) of the second ring groove (6) is 30° to 60° and a percentage of a value (C/D) obtained by dividing a depth (C) of the tapered face (14) in a radial direction of the piston by a depth (D) of the second ring groove (6) in the radial direction of the piston is 20% to 30%, it is possible to stably and sufficiently reduce oil consumption and the leakage of the blow-by gas even after prolonged operation for a long period of time.
If the angle (Θ) of the tapered face (14) is too small or the percentage of the value (C/D) related to the depth (C) of the tapered face (14) is too small, the capacity of the indentation (13) of the second land (5) becomes small, the capacity of the space (17) facing the second land does not sufficiently increase, and it is difficult to suppress effectively the variation in the gas pressure in the space (17) facing the second land during the upward and downward movements of the piston, and the first pressure ring (10) and the second pressure ring (11) arc liable to vibrate.
On the other hand, if the angle (Θ) of the tapered face (14) is too large, a large area of the second land (5) in the width (W2) direction is trimmed off to form the tapered face (14), the rigidity of the second land (5) is reduced, the piston (18) is more liable to vibrate, the first ring groove (4) and the second ring groove (6) become liable to deformation and excessive wear, and the first pressure ring (10) and the second pressure ring (11) become liable to vibrate.
If the percentage of the value (C/D) related to the depth (C) of the tapered face (14) is too large, the area of the second ring groove (6) available for supporting the second pressure ring (11) becomes too small and the second pressure ring (11) becomes liable to vibrate.
As described above, if the angle (Θ) of the tapered face (14) and the percentage of the value (C/D) related to the depth (C) of the tapered face (14) are outside the optimum ranges, at least one of the first pressure ring (10) and the second pressure ring (11) becomes liable to vibrate and it may be impossible to sufficiently reduce the oil consumption and the leakage of the blow-by gas in some cases due to degradation of the sealing performance of the first pressure ring (10) and/or the second pressure ring (11).
As shown as an example in Fig. 1B, the percentage of the value (W2/B) obtained by dividing the width (W2) of the second land (5) by the diameter (B) of the cylinder bore is preferably 6% to 15% to promote stable and sufficient reduction of the oil consumption and leakage of the blow-by gas even after prolonged operation.
If the value (W2/B) related to the width (W2) of the second land (5) is too small, outside the optimum range, the capacity of the space (17) facing the second land becomes small, it is difficult to effectively suppress the variation in the gas pressure in the space (17) facing the second land during the upward and downward movements of the piston, the first pressure ring (10) and the second pressure ring (11) become liable to vibrate, and it may be impossible to sufficiently reduce the oil consumption and the leakage of the blow-by gas in some cases due to degradation of the sealing performance of the first pressure ring (10) and the second pressure ring (11).
On the other hand, if the percentage of the value (W2/B) related to the width (W2) of the second land (5) is too large outside the optimum range, the overall length of the piston (18) may become greater than an appropriate value in some cases.
As shown as an example in Fig. 1B, an indentation (15) of the third land (7) is formed at a boundary between an outer peripheral face (7a) of the third land (7) and a third-land-side end face (8a) of the third ring groove (8), a capacity of a space (20) facing the third land increases by a capacity of the indentation (15) of the third land (7). This promotes the suppression of variation in the gas pressure in the space (20) facing the third land during the upward and downward movements of the piston. It also helps to suppress the vibration of the second pressure ring (11) and the oil ring (12), and promotes reduction of oil consumption amount and leakage of the blow-by gas due to consequent improvement in the sealing performance of the second pressure ring (11) and the oil ring (12).
As shown in Fig. 1(B), an indentation (16) of the piston skirt (9) is formed at a boundary between an outer peripheral face (9a) of the piston skirt (9) and a piston-skirt-side end face (8b) of the third ring groove (8). This feature assists in the reduction of oil consumption , because part of the oil scraped off by a lower portion of the oil ring (12) becomes likely to be introduced into the piston (18) through the indentation (16) of the piston skirt (9), an oil inlet (35), the third ring groove (8), and an oil outlet (36) and return into an oil pan (not shown) at a lower portion of the engine and the oil can be discharged quickly.

Detailed description

As shown in Fig. 1A, in the engine (21), a piston (18) is fitted in a cylinder (22) to be able to move up and down and a crankshaft (24) is interlinked with the piston (18) with a connecting rod (23) interposed therebetween. A cylinder head (25) is mounted to an upper portion of the cylinder (22). In the cylinder head (25), an intake port (26), an exhaust port (27), and a fuel injection nozzle (28) are formed. A reference numeral (1a) in the drawings designates a centre axis of the piston.
As shown in Fig. 1B, a first land (3), a first ring groove (4), a second land (5), a second ring groove (6), a third land (7), a third ring groove (8), and a piston skirt (9) are formed on a piston peripheral wall (1) in this order from a side of a piston head (2). A first pressure ring (10) is fitted in the first ring groove (4), a second pressure ring (11) is fitted in the second ring groove (6), an oil ring (12) is fitted in the third ring groove (8), and an indentation (13) is formed in the second land (5).
As shown in Fig. 1B, a corner at a boundary between an outer peripheral face (5a) of the second land (5) and a second-land-side end face (6a) of the second ring groove (6) is bevelled, and in particular planed off with a tapered face (14) having a diameter reducing toward the second ring groove (6) and the tapered face (14) forms the indentation (13) of the second land (5).
As shown in Fig. 1B, the angle (Θ) of the tapered face (14) with respect to a cylinder-side imaginary extension line (6b) of the second-land-side end face (6a) of the second ring groove (6) is preferably 30° to 60° (more preferably, 40° to 50°) and the percentage value (C/D) obtained by dividing a depth (C) of the tapered face (14) in a radial direction of the piston by a depth (D) of the second ring groove (6) in the radial direction of the piston is preferably 20% to 30%. These are the optimum ranges of the angle (Θ)of the tapered face (14) and the percentage of the value (C/D) related to the depth of the tapered face (14).
As shown in Fig. 1B, the value (W2/B) obtained by dividing a width (W2) of the second land (5) by a diameter (B) of a cylinder bore is preferably in an optimum range from 6% to 15%.
One reason why the ratio of the width (W2) of the second land (5) to the diameter (B) of the cylinder bore is calculated is that the diameter (B) of the cylinder bore provides indications of a size and combustion chamber pressure of the engine. The size and the combustion chamber pressure of the engine greatly affect the oil consumption of the engine and the leakage of the blow-by gas.
As shown in Fig. 1B, an indentation (15) in the third land (7) is formed at a boundary between an outer peripheral face (7a) of the third land (7) and a third-land-side end face (8a) of the third ring groove (8).
Furthermore, an indentation (16) of the piston skirt (9) is formed at a boundary between an outer peripheral face (9a) of the piston skirt (9) and a piston-skirt-side end face (8b) of the third ring groove (8).
The indentation (15) of the third land (7) is formed by a groove (29) in the shape of a right-angled L in a sectional view along the centre axis (1a) of the piston, a back end face (30) of the indentation (15) is parallel to the center axis (1a) of the piston, and a face (31) of the indentation (15) and on a side of the piston head (2) is in an orientation orthogonal to the center axis (1a) of the piston.
The indentation (16) of the piston skirt (9) is formed by a groove (32) in a shape of an obtuse-angled L shape in a sectional view along the center axis (1a) of the piston, a back end face (33) of the indentation (16) is parallel to the center axis (1a) of the piston, and a face (34) of the indentation (16) and on an opposite side from the piston head (2) is formed as a tapered face having a diameter reducing toward the back end face (33).
As shown in Fig. 1B, an oil inlet (35) passing through the oil ring (12) is formed in the oil ring (12) along the radial direction of the piston and an oil outlet (36) passing through the piston peripheral wall (1) along the radial direction of the piston is formed in a back end of the third ring groove (8). Oil scraped off the cylinder (22) by the oil ring (12) is introduced into the piston (18) through the oil inlet (35), the third ring groove (8), and the oil outlet (36) and returns into an oil pan (not shown) at a lower portion of the engine.
As compared with comparative engines outside the above-described optimum ranges according to the first embodiment, exemplary engines in the optimum ranges obtained the following satisfactory experimental results with regard to the oil consumption and the leakage of the blow-by gas.
A first experiment was conducted by using a vertical water-cooled in-line four-cylinder direct-injection diesel engine with a cylinder bore diameter (B) of 87 mm, a maximum diameter (P) of a piston head (2) of 86.5 mm, a minimum diameter of the piston head (2) of 86.46 mm, a piston axial length (L) of 80 mm, and a piston stroke of 102.4 mm at 20°C and by running the engine at an engine speed of 2700 rpm and with a load factor of 80% for 200 hours. The load factor was calculated with respect to a load factor of 100% representing a rated load at a rated speed at which a maximum output can be obtained.
As the exemplary engines, a minimum-value exemplary engine using respective minimum values in the above-described optimum ranges, a maximum-value exemplary engine using respective maximum values, and an intermediate-value exemplary engine using respective intermediate values were produced.
As the comparative engines, engines without tapered faces (14) which exist in the respective exemplary engines were produced.
They were compared to each other and it was found that oil consumptions reduced by about 30% and leakages of blow-by gas reduced by about 35% in the respective exemplary engines from the respective comparative engines. No major degradation of performance was found after the operation for 200 hours.
In the minimum-value exemplary engine, the angle (Θ) of the tapered face (14) was 30°, the value (C/D) related to a depth (D) in a piston diameter direction was 20%, and the value (W2/B) related to a width (W2) of a second land (5) was 6%.
In the maximum-value exemplary engine, the angle (Θ) of the tapered face (14) was 60°, the value (C/D) related to a depth (D) in a piston diameter direction was 30%, and the value (W2/B) related to a width (W2) of a second land (5) was 11%.
In the intermediate-value exemplary engine, the angle (Θ) of the tapered face (14) was 45°, a the value (C/D) related to a depth (D) in a piston diameter direction was 25%, and the value (W2/B) related to a width (W2) of a second land (5) was 8.5%.
In each of the engines, the value (W1/B) obtained by dividing a width (W1) of a first land (3) by the cylinder bore diameter (B) was 13%. A value (W3/B) obtained by dividing a width (W3) of a third land (7) by the cylinder bore diameter (B) was 4%.
Comparative engines in which only the taper angles (Θ) in the respective exemplary engines were changed to 25° (smaller than the lower limit, 30° in the appropriate range) were produced.
The respective exemplary engines and the respective comparative engines were compared to each other and it was found that the oil consumptions reduced by about 15% and the leakages of blow-by gas reduced by about 17% in the respective exemplary engines from the respective comparative engines.
Comparative engines in which only the taper angles (Θ) in the respective exemplary engines were changed to 65° (larger than the upper limit, 60° in the appropriate range) were produced.
The respective exemplary engines and the respective comparative engines were compared to each other and it was found that the oil consumptions reduced by about 15% and the leakages of blow-by gas reduced by about 17% in the respective exemplary engines from the respective comparative engines.
Comparative engines in which only the values (C/D) related to the depths (C) of the tapered faces (14) in the respective exemplary engines were changed to 10% (lower than the lower limit, 20% in the appropriate range) were produced.
The respective exemplary engines and the respective comparative engines were compared to each other and it was found that the oil consumptions reduced by about 20% and the leakages of blow-by gas reduced by about 23% in the respective exemplary engines from the respective comparative engines.
Comparative engines in which only values (C/D) related to the depths (C) of the tapered faces (14) in the respective exemplary engines were changed to 40% (higher than the upper limit, 30% in the appropriate range) were produced.
The respective exemplary engines and the respective comparative engines were compared to each other and it was found that the oil consumptions reduced by about 20% and the leakages of blow-by gas reduced by about 23% in the respective exemplary engines from the respective comparative engines.
Comparative engines in which only the values (W2/B) related to the widths (W2) of the second land (5) in the respective exemplary engines were changed to 5% (lower than the lower limit, 6% in the appropriate range) were produced.
The respective exemplary engines and the respective comparative engines were compared to each other and it was found that the oil consumptions reduced by about 15% and the leakages of blow-by gas reduced by about 17% in the respective exemplary engines from the respective comparative engines.
Moreover, it was found that an overall length of the piston (18) exceeded an appropriate length if only the values (W2/B) related to the widths (W2) of the second land (5) in the respective exemplary engines were changed to 12% (higher than 11%, the upper limit value in the appropriate range).
Preferably, the value (W1/B) obtained by dividing the width (W1) of the first land (3) by the cylinder bore diameter (B) is set to 8% or higher and the value (W3/B) obtained by dividing the width (W3) of the third land (7) by the cylinder bore diameter (B) is set to 2% or a higher. Under these percentages, the capacities of a space (19) facing the first land and a space (20) facing the third land become small, the oil and the blow-by gas become liable to pass through the space (19) facing the first land and the space (20) facing the third land, and it may be impossible to effectively reduce the oil consumption and the leakage of the blow-by gas in some cases.
Preferably, the (percentage) sum of the value (W1/B) related to the width (W1) of the first land (3), the value (W2/B) related to the width (W2) of the second land (5), and value (W3/B) related to the width (W3) of the third land (7) is 28% or lower. If the sum exceeds this percentage, the overall length of the piston (18) may become greater than the appropriate value in some cases.
A second experiment was conducted by using a vertical water-cooled in-line four-cylinder indirect-injection diesel engine with a cylinder bore diameter (B) of 78 mm, a maximum diameter (P) of a piston head (2) of 77.5 mm, a minimum diameter of the piston head (2) of 77.46 mm, a piston axial length (L) of 70 mm, and a piston stroke of 78.4 mm at 20°C and by running the engine at an engine speed of 3000 rpm and with a load factor of 80% for 200 hours.
The second experiment was conducted by using exemplary engines and comparative engines adjusted to have the same dimensional ratios as in the first experiment and equivalent experimental results to those of the first experiment were obtained.
As shown in Fig. 2(B), in a second embodiment, a corner at a boundary between an outer peripheral face (7a) of a third land (7) and a third-land-side end face (8a) of a third ring groove (8) is bevelled i.e. planed off with a tapered face (37) having a diameter reducing toward the third ring groove (8) and the tapered face (37) forms an indentation (15) of the third land (7).
As shown in Fig. 2B, the angle (α) of the tapered face (37) with respect to a cylinder-side imaginary extension line (8b) of the third-land-side end face (8a) of the third ring groove (8) is preferably 30° to 60° (more preferably, 40° to 50°). The value (E/F) obtained by dividing a depth (E) of the tapered face (37) in a radial direction of the piston by a depth (F) of the third ring groove (8) in the radial direction of the piston is preferably 20% to 30%. These are the optimum ranges of the angle (α)and the value (E/F).
Similarly to the tapered face (14) of the second land (5), the tapered face (3 7) of the third land (7) in these optimum ranges can stably and sufficiently reduce the oil consumption and the leakage of the blow-by gas even after prolonged operation. Outside these optimum ranges, a second pressure ring (11) and an oil ring (12) become liable to vibrate and it may be impossible to sufficiently reduce the oil consumption and the leakage of the blow-by gas due to degradation of sealing performance of the second pressure ring (11) and the oil ring (12) in some cases.
In the second embodiment, as in the first embodiment, an indentation (16) of a piston skirt (9) is formed at a boundary between an outer peripheral face (9a) of the piston skirt (9) and a piston-skirt-side end face (8b) of the third ring groove (8). However, the shape of the indentation (16) of the piston skirt (9) is different from that in the first embodiment and is formed by a right-angled L-shaped groove (38) in a sectional view along a centre axis (1a) of a piston. A back end face (33) of the indentation (16) is parallel to the center axis (1a) of the piston and a face (34) of the indentation (16) and on an opposite side from a piston head (2) is in an orientation orthogonal to the center axis (1a) of the piston.
The other structures are the same as those in the first embodiment and the same components as those in the first embodiment are provided with the same reference numerals in Figs. 2A and 2B.
The same experiments as those on the engine according to the first embodiment were conducted on the engine according to the second embodiment and equivalent results to those in the first embodiment were obtained.

Claims

An engine comprising: a first land (3), a first ring groove (4), a second land (5), a second ring groove (6), a third land (7), a third ring groove (8), and a piston skirt (9) formed on a piston peripheral wall (1) in this order from a side of a piston head (2); a first pressure ring (10) fitted in the first ring groove (4); a second pressure ring (11) fitted in the second ring groove (6); an oil ring (12) fitted in the third ring groove (8); and an indentation (13) formed at the second land (5),
characterised in that a corner at a boundary between an outer peripheral face (5a) of the second land (5) and a second-land-side end face (6a) of the second ring groove (6) is planed off with a tapered face (14) having a diameter reducing toward the second ring groove (6) and the tapered face (14) forms the indentation (13) of the second land (5).
An engine according to claim 1, wherein an angle (Θ) of the tapered face (14) to a cylinder-side imaginary extension line (6b) of the second-land-side end face (6a) of the second ring groove (6) is from 30° to 60° and value (C/D) obtained by dividing a depth (C) of the tapered face (14) in a radial direction of a piston by a depth (D) of the second ring groove (6) in the radial direction of the piston is 20% to 30%.
An engine according to claim 2, wherein a value (W2B) obtained by dividing a width (W2) of the second land (5) by a cylinder bore diameter (B) is from 6% to 11 %.
An engine according to any of claims 1 to 3 and further comprising an indentation (15) at the third land (7) and formed at a boundary between an outer peripheral face (7a) of the third land (7) and a third-land-side end face (8a) of the third ring groove (8).
An engine according to any of claims 1 to 4 and further comprising an indentation (16) at the piston skirt (9) and formed at a boundary between an outer peripheral face (9a) of the piston skirt (9) and a piston-skirt-side end face (8b) of the third ring groove (8).
A piston for a diesel engine, comprising: a first land (3), a first ring groove (4), a second land (5), a second ring groove (6), a third land (7), a third ring groove (8), and a piston skirt (9) formed on a piston peripheral wall (1) in this order from a side of a piston head (2); a first pressure ring (10) fitted in the first ring groove (4); a second pressure ring (11) fitted in the second ring groove (6); an oil ring (12) fitted in the third ring groove (8); and an indentation (13) formed at the second land (5),
characterised in that a corner at a boundary between an outer periplaexal face (5a) of the second land (5) and a second-land-side end face (6a) of the second ring groove (6) has a bevelled face (14) having a diameter reducing toward the second ring groove (6) and the tapered face (14) forms the indentation (13) of the second land (5).
A piston according to claim 6, wherein an angle (Θ) of the tapered face (14) to a cylinder-side imaginary extension line (6b) of the second-land-side end face (6a) of the second ring groove (6) is from 30° to 60° and value (C/D) obtained by dividing a depth (C) of the tapered face (14) in a radial direction of a piston by a depth (D) of the second ring groove (6) in the radial direction of the piston is 20% to 30%.
A piston according to claim 7 wherein a value (W2/B) obtained by dividing a width (W2) of the second land (5) by a cylinder bore diameter (B) is from 6% to 11%.
A piston according to any of claims 6 to 8, and further comprising an indentation (15) at the third land (7) and formed at a boundary between an outer peripheral face (7a) of the third land (7) and a third-land-side end face (8a) of the third ring groove (8).
A piston according to any of claims 6 to 9 and further comprising an indentation (16) at the piston skirt (9) and formed at a boundary between an outer peripheral face (9a) of the piston skirt (9) and a piston-skirt-side end face (8b) of the third ring groove (8).